What is a canonical tag?
A canonical tag is implemented in HTML and tells search engines, such as Google, the master version of your webpage. The tag is found frequently inside an <link> element within the <head> of each document.
An excellent example of when to use canonical tags is when using URL Parameters to sort category content. For example, let’s pretend we have these two URLs:
Both of these pages might include the same material, but one sorts it by the default sorting, while the other sorts by price. Telling search engines that these are the same page helps to prevent cannibalisation and duplication. It also helps to funnel links toward a single page.
How can I check my canonical tags?
Checking canonical tags is simple. First, you can search “canonical” in the source code to see if there are any matches. This technique allows you to check page-by-page canonical tags.
Another more sophisticated way to check for canonical tags is to use Screaming Frog. First, crawl the website or list of pages that you would like to review. Afterwards, you will need to check the canonical tab.
If the page canonicalises toward another, then the indexability column will read “canonicalised”. This method allows you to quickly check your entire site to find issues with canonical tags.
If you do not have access to Screaming Frog, then you can use Google Search Console to check for issues with canonical tags. To do this, you will need to open up the Index Coverage Report.
The first issue that you will likely find in the Excluded data is the “Duplicate without user-selected canonical” pages. These pages are marked by Google as being duplicate content and have no canonical tag.
The second issue that you are likely to find is the “Duplicate; Google chose different canonical than user”.
In this instance, you have specified a canonical tag, but Google decided this was either done in error or that there was a better match. For example, if you had set up your URL Parameters with self-referential canonical tags, they may be ignored.
In this situation, Google would prefer to pass the canonical toward the default page on your behalf. However, if you want to improve your autonomy, you should set this yourself to make sure it’s always appropriately configured.
How can I improve canonicalisation?
By default, Google considers the lack of a canonical to be the same as self-referential canonical tags. Therefore, even without any optimisation, your pages should be covered by most search engines.
If you would like to assist Google further, you can include a self-referential canonical tag for each page. It allows Google to see that you have clearly stated this is the master version of the page.
Lastly, if you are using URL parameters and want to specify the original page, these should all canonicalise to the default version. Google has stated that it treats all of these pages like a singular page.
Should I add noindex to canonicalised URLs?
No, the use of canonical tags suggests to Google that one page is the original version of two nearly identical pages. However, if you are trying to canonicalise pages that are different – a noindex tag would be better.
You can find out more about how canonical tags and noindex tags work together in this short video: